The intestinal epithelium in most species of animals, utilizes blood glutamine as an important respiratory substrate, in vivo. The contribution of glutamine to the energetics, metabolism, and synthetic controls of epithelium is being examined in several in vitro preparations including tissue slices, isolated epithelial cells, mitochondria, everted sacs, and organ cultures. Intestinal segments from rat, guinea pig, rabbit, chicken, and other animals can metabolize glutamine to CO2, glutamate, organic acids, and amino acids. The products formed are to be analyzed. The relative importance of mitochondrial phosphate -dependent glutaminase, transaminases, glutamate dehydrogenase, and other enzymes in the observed metabolism is to be evaluated. The ability of added glutamine, ketone bodies, and other metabolites to promote the viability of intestine, in vitro, is under study. Metabolic inhibitors such as the glutamine analogs, 6-diazo-5-oxo-L-norleucine and 5-chloro-4-oxo-L-norvaline, can block glutamine metabolism by inhibiting the phosphate-dependent glutaminase in villus and crypt cells. Such preparations can be of value in studies of glutamine transport and alternate pathways of metabolism.